A communication system includes a DownLink (DL) that conveys signals from one or more Transmission Points (TPs) to User Equipments (UEs), and an UpLink (UL) that conveys signals from UEs to one or more Reception Points (RPs). A UE, also commonly referred to as a terminal or a mobile station, may be fixed or mobile and may be a wireless device, a cellular phone, a personal computer device, etc. A TP or a RP is generally a fixed station and may also be referred to as a Base Transceiver System (BTS), a Node B, an enhanced Node B (eNB), an access point, etc.
A communication system also supports the transmission of several signal types for its proper functionality including data signals conveying information content, control signals enabling proper processing of data signals, and Reference Signals (RS), also known as pilots, enabling coherent demodulation of data or control signals or providing Channel State Information (CSI) corresponding to an estimate of the channel medium experienced by their transmission.
UL data information is conveyed through a Physical UL Shared CHannel (PUSCH). UL Control Information (UCI) is conveyed through a Physical UL Control CHannel (PUCCH) unless a UE also has a PUSCH transmission in which case the UE may convey at least some UCI together with data information through the PUSCH. The UCI includes ACKnowledgment information associated with the use of a Hybrid Automatic Repeat reQuest (HARM) process. The HARQ-ACK is in response to the reception by the UE of Transport Blocks (TBs) in the DownLink (DL) of the communication system, which corresponds to signal transmission from the Node B to the UE. The DL TBs are transmitted through a Physical Downlink Shared CHannel (PDSCH). The UCI may also include Channel Quality Indicator (CQI), or Precoding Matrix Indicator (PMI), or Rank Indicator (RI), which may be jointly referred to as Channel State Information (CSI). The CQI provides to the Node B a measure of the Signal to Interference and Noise Ratio (SINR) the UE experiences over sub-bands or over the whole operating DL BandWidth (BW). This measure is typically in the form of the highest Modulation and Coding Scheme (MCS) for which a predetermined BLock Error Rate (BLER) can be achieved for the transmission of TBs. The PMI/RI informs the Node B how to combine the signal transmission to the UE from multiple Node B antennas in accordance with the Multiple-Input Multiple-Output (MIMO) principle. A UE may transmit UCI either separately from data information in a Physical Uplink Control CHannel (PUCCH) or together with data information in a Physical Uplink Shared CHannel (PUSCH).
DL data information is conveyed through a Physical DL Shared CHannel (PDSCH). DL Control Information (DCI) includes DL CSI feedback request to UEs, Scheduling Assignments (SAs) for PUSCH transmissions from UEs (UL SAs) or for PDSCH receptions by UEs (DL SAs). The SAs are conveyed through DCI formats transmitted in respective Physical DL Control CHannels (PDCCHs). In addition to SAs, PDCCHs may convey DCI that is common to all UEs or to a group of UEs.
DCI also includes HARQ-ACK information that one or more TPs transmit to UEs through Physical HARQ-ACK Indicator CHannels (PHICHs) in response to respective receptions of data TBs transmitted from the UEs to RPs.
Typically, the PDCCHs are a major part of the total DL overhead. One method for reducing this overhead is to scale its size according to the resources required to transmit the PDCCHs and PHICHs. Assuming Orthogonal Frequency Division Multiple Access (OFDMA) as the DL transmission method, a Control Channel Format Indicator (CCFI) parameter can be transmitted through the Physical Control Format Indicator CHannel (PCFICH) to indicate the number of OFDM symbols allocated to the DL control region during a DL Transmission Time Interval (TTI).